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38 | Chapter 2. Configuring System Information
ProSafe® Gigabit L3 Managed Stackable Switches Software Administration Manual
Time
ProSafe® Managed Switches software supports the Simple Network Time Protocol (SNTP).
You can also set the system time manually
SNTP assures accurate network device clock time synchronization up to the millisecond.
Time synchronization is performed by a network SNTP server. ProSafe® Managed Switches
software operates only as an SNTP client and cannot provide time services to other systems.
Time sources are established by Stratums. Stratums define the accuracy of the reference
clock. The higher the stratum (where zero is the highest), the more accurate the clock. The
device receives time from stratum 1 and above since it is itself a stratum 2 device.
The following is an example of stratums:
• Stratum 0: A real-time clock is used as the time source, for example, a GPS system.
• Stratum 1: A server that is directly linked to a Stratum 0 time source is used. Stratum 1
time servers provide primary network time standards.
• Stratum 2: The time source is distanced from the Stratum 1 server over a network path.
For example, a Stratum 2 server receives the time over a network link, via NTP, from a
Stratum 1 server.
Information received from SNTP servers is evaluated based on the time level and server
type.
SNTP time definitions are assessed and determined by the following time levels:
• T1: Time at which the original request was sent by the client.
• T2: Time at which the original request was received by the server.
• T3: Time at which the server sent a reply.
• T4: Time at which the client received the server's reply.
The device can poll Unicast server types for the server time.
Polling for Unicast information is used for polling a server for which the IP address is known.
SNTP servers that have been configured on the device are the only ones that are polled for
synchronization information. T1 through T4 are used to determine server time. This is the
preferred method for synchronizing device time because it is the most secure method. If this
method is selected, SNTP information is accepted only from SNTP servers defined on the
device using the SNTP Server Configuration page.
The device retrieves synchronization information, either by actively requesting information or
at every poll interval.
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